the eloisatron: physics at the energy...

US Particle Accelerator School!1

The Eloisatron: Physics at the Energy Frontier

William A. Barletta Dept. of Physics, MIT

Economics Faculty, University of Ljubljana Director, US Particle Accelerator School


I am pleased join illustrious colleagues to speak in tribute to Antonino Zichichi

about a topic central to his interests for decades and that I have also described as my church

Of course I am referring to Nino s grand vision of the Eloisatron

a Galilean tool to explore physics at the highest energies and luminosities


Early steps toward ELN have lasting impact

!! 1976 - International School of Accelerator Physics at Erice "! Directly led to establishing the USPAS and the CERN School

Result: Blossoming of education in accelerator science

!! 1979 - Superconducting Cyclotron Project resumed "! 1981 Start of the CS construction (Ansaldo-LMI-Zanon)

Result: Cyclotrons remain a strong tool for discovery physics

!! 1981 - HERA Project is presented to the INFN Council "! Critical insight: Involve industrial labs very early in the R&D "! 1985 Begin construction in Italy of prototype superconducting

magnets for HERA "! 1988 Complete construction of the HERA magnets

Result: Industry plays a critical role in magnet R&D

A. Zichichi, The Superworld II - 1990!


Like Saul on the road to Damascus I recall the time and place of my conversion:

Nino’s challenge to me led

to my long involvement in trying to realize his vision


Thirty years ago: (1984-1988) INFN finances ELOISATRON (ELN) Project

!! Full Scale ELOISATRON PROJECT: "! 1st step - Conceptual Design Report (Kjell Johnson) "! 2nd - R&D in fundamental technologies "! 3rd - Construction of long (15 m) superconducting magnets

!! 1989 Start model magnet construction for 10% ELN By 1992 feasibility of LHC magnets was demonstrated

!! 1991, 1992 ELN conceptual design workshop 1 Feedback systems from ALS can scale to 100 TeV protons

!! 1991, 1992 ELN conceptual design workshop 1 & 2 No fundamental obstacle to 200 TeV collider at 1035 cm-2s-1

!! 1995, 1999 ELN workshops on magnets beyond the LHC Inspired the 2001 US multi-lab study of VLHC


Key insights in the original ELN plan

!! Authentic innovations stem from the discovery of new, fundamental Laws of Nature. "! This is a field where Italy has engaged its intellectual forces..

!! It is not a wise idea to wait for new ideas "! It takes a long time to transform new ideas into reality

•! 25 years from SC magnets to the Tevatron

!! Do not start to build a new Laboratory if the work needed can be carried out within existing structures

!! Involve Industry in the implementation of the project.



Key technological insights in ELN project

!! We know how to build a proton synchrotron for 100 TeV

!! Invest in R&D to learn how to build an adequate detector "! Hermeticity is important

!! Build a large tunnel (300 km) "! Minimize the magnet & vacuum challenges "! Minimize costs "! Maximize the potential of the facility

!! Devote equal effort to experimental set-ups & to machine construction


ELN - 300 km (1985)!

Focused engineering development is no substitute for innovative R&D


Fast-forward to the present

Then move forward to the future


“If there is a desert, it is a desert of our imagination” - Nino it is a desert of our imagination” it is a desert of our imagination”

ELN!

Accelerator-based physics: Origin of Mass, Beyond Standard Model (BSM), Superworld Astrophysics: BSM physics , The Dark Universe

Relic radiation: Neutrino astronomy, quantum gravity


ELN => decades of forefront particle physics

!! Large interest worldwide in a 100-TeV-class pp collider "! Interest in any LHC energy upgrade depends on results from

Run-II & on developing practical magnet technology at !16 T

!! A new collider should be a large advance beyond LHC "! The last big tunnel "! Multi-step scenarios are the most realistic "! Eventually 50 to >100 TeV per beam

!! Discovery potential far surpasses that of lepton colliders "! Much higher energy plus high luminosity "! The only sure way to the next energy scale


As long as Standard Model continues to work, Higher energy is always better - Zichichi

!! What is the cost vs benefit for "! Higher energy "! Higher luminosity "! What is the Energy vs Luminosity tradeoff?

!! Physics case studies must generate answers to these questions

!! Naturalness arguments push towards higher masses => higher energy "! Collider energy wins rapidly at higher masses

!! Dark Matter, electroweak baryogenesis may relate to physics at lower masses & smaller coupling ==> high luminosity is more important

"! At 100 TeV, 10x increase in luminosity ==> 7 TeV increase in mass reach

!! For a 100 TeV scale collider, discovery luminosity ~2x1035

"! Studies of high mass particle will need ~10x more luminosity

Different physics call for different optimizations

I. Hinchcliffe et.al.; arXiv:1504.06108


“The machine should be designed with the highest possible luminosity & energy” - Nino


Nino cautioned: Detectors need R&D Present view of detector challenges echoes Nino

!! Measure all detectable particles over as much of the angular phase space as possible

!! Minimize reducible backgrounds from misidentified particles "! Hermeticity is important

!! Enable data-taking in high instantaneous luminosity environment "! Very large track multiplicity, hundreds of uninteresting events per crossing "! Total exposure of sensors to radiation flux scales with integrated luminosity

& falls off with distance from collision point •! Radiation damage degrades sensor efficiency & increases noise

!! Undetectable particles like neutrinos & Dark Matter can only have their transverse momentum sum inferred "! Catch all visible momentum; impose transverse momentum conservation "! Hermeticity is important


Discovery science requires discovery technology

New detectors!


1.! Beam Energy "! Determines the energy scale of phenomena to be studied

2.! Luminosity L (collision rate) "! Determines the production rate of interesting events

"! Scale L as E2 to maximize discovery potential at a given energy

•! Conventional Wisdom: 2x in energy is worth 10x in luminosity

What sets the discovery potential of colliders?

L= N1 ! N2! frequencyOverlap Area

=N1 ! N2! f

4!" x! y !Disruption ! angle correction

Note: L changes in time as collisions deplete the bunches!!==> Luminosity lifetime !


Assume that bunch length, !z < "* (depth of focus)!Neglect corrections for crossing angle

#

Set N1 = N2 = N

Collision frequency = ("tcoll)-1 = c/SBunch!

Luminosity:!The fundamental challenge of the energy frontier!

Other parameters remaining equal!

L nat $ Energy !but L required $ (Energy)2!

Pain associated with going to higher energy grows non-linearly!

Most pain is associated with increasing beam currents.!

L =N 2c!

4"#n!*SB

=1

erimic2

Nri4!"n

EI!*

!

"#

$

%&=

1erimic

2

Nri4!"n

Pbeam!*

!

"#

$

%& i = e,p

Linear or Circular!

Tune shift!


CERN FCC - 100 km!

China -77 km!

Texas - 270 km!

One irreversible decision: the radius of the collider tunnel

VLHC - 233 km!

ELN !300 km!


What drives parameter choices?!

!! How do we choose N, SB, "*, and %n as a function of energy? !"! Detector considerations!

•! Near zero crossing angle!•! Electronics cycling # 20 ns between crossings !•! Event resolution $ 1 event/crossing!•! Radiation damage!

"! Accelerator physics!•! Tune shifts - keep N small, lower SB, lower %n !•! Beam instabilities - keep N small, lower SB, lower %n !•! Luminosity lifetimes - raise N, raise %n, !•! Emittance control - raise N, raise %n !•! Synchrotron radiation handling - Keep I small!•! Radiation damage!


Crucial detector issue is coupled to collider design: Bunch spacing vs. event pile-up

n = L !inel SBc

L k = L n k exp - n k ! !

Most probable # events per crossing!

Fractional luminosity for k events per crossing!

!inel ~ ln Ecm!

20 TeV per beam!

20 ns Possible with !

modern trigger electronics!

5 ns

At 200 TeV and 2x1035cm-2s-1 we expect ~600 events per crossing at 20 MHz!


Resetting electronics every 5 ns demands increasing crossing angle of beams

!! Minimum bunch spacing is set by filling every rf-bucket!•! BUT, to avoid excessive long rang tune shift, "&LR !==> larger crossing angle, ' ==> decreased hermeticity

!!LR = !!HO 2nLR "#

* $ 2

! ! HO = N B rp

4 " "n

3 2 1 1 2 3

Debris!

At 20 ns spacing ~ 10 - 20% effect!

!

"# tot = NIP 1+ 2nLR $%*&

'

( )

*

+ ,

2-

. / /

0

1 2 2 "# HO

(&tot#

SB!

For I, ' = constant!


Components that limit energy & luminosity !

!! Main ring!"! Dipoles - bend beam in circle "! Feedback- stabilizes beam against instabilities ( ~NBI) "! Vacuum chamber - keeps atmosphere out "! Cooling - removes waste heat "! Beam dumps & aborts - protects machine and detectors

!! Interaction Regions and detectors!"! Quadrupoles to focus beam!"! Septa to decouple beams electromagnetically!"! Detector to do particle physics (via radiation damage)


Three design strategies for ELN

!! Low field (2T), superferric magnets "! Very large tunnel & very large stored beam energy "! Minimal influence of synchrotron radiation

!! Medium field design "! Large tunnel & large stored beam energy "! Uses ductile superconductor at 4 - 7 T (RHIC-like) "! Some luminosity enhancement from radiation damping

!! High field magnets with brittle superconductor (>10 T) "! Maximizes effects of synchrotron radiation "! Highest possible energy in given size tunnel "! Greatest technical risk and greatest cost

Does synchrotron radiation raise or lower the collider $/TeV?


Cost drivers set design & R&D priorities (based on SSC green field experience)

Lowering dipole cost is the key to cost control

Build at an existing hadron laboratory

Total cost!

Accelerator cost distribution

SSC! Accelerator ! &! Experiments!

$ ~ B-1!

existing hadron laboratory

Total cost

Accelerator cost distribution

Note: The cost per T-m !increases with B!


Proton colliders beyond 14 TeV: CERN is leading 100 km tunnel collider study

!! Reach of an LHC energy upgrade is very limited (~26 TeV) "! No engineering materials beyond Nb3Sn (Practical limit <16 T) "! Synchrotron radiation management is challenging

!! Proton colliders at 50 - 100 TeV "! US multi-lab study of VLHC (circa 2001) is still valid - 233 km ring

Breakpoints in technology are also breakpoints in cost [1::8::20(?) per kA-m]cern!

!

Pprot on (kW ) = 6.03 E(TeV )4 I(A)

"(m)

Breakpoints in technology are also breakpoints in cost [1::8::20

SR< 3 W/m

SR>20 W/m

SR~1.2 W/m


Proton colliders: Magnets

!! For a 100 TeV machine: »! 270 km requires 4.5 T »! 100 km requires 16 T

!! LHC dipoles operate at 8T * »!

25

* Level at which all dipoles operate reliably, less than the highest test field.

!! The LHC dipoles are wound with Nb-Ti. »! They are industrialized, but expensive »! ~1/2 total cost of collider ring

!! 16 T magnets will require Nb3Sn or HTS (or both)


At > 50 TeV/beam : Synchrotron radiation dominates beam physics

!! Radiation damping of emittance increases luminosity "! Maybe eases injection "! Maybe loosen tolerances

==> Saves money ?

!! Energy loss via SR limits Ibeam "! 1 - Increases rf-power to replace beam energy "! 2 - Heats walls => cryogenic heat load => wall resistivity ==> instability "! 3 - Photo-desorption => beam-gas scattering => quench of SC magnets

==> Costs money

increases luminosity

-power to replace beam energy

E = 88 TeV Bd = 9.8 T To = 2.5 h

Does synchrotron radiation raise or lower the collider !/TeV?


Vacuum/cryo systems are surprizingly expensive Scaling LHC is not an option

!! Beam screen for high field options "! Increases required aperture & cost "! Physical or chemical absorption

•! Requires annual regeneration

!! Cryogenics "! Superfuild systems are impractical at this

scale

!! Let photons escape in low field option "! No conductor in mid-plane "! Warm bore / ante-chambers

Managing synchrotron radiation power becomes challenging as Psr >5 W/m


Scaling of radiation from hadronic shower !

!! Power in charged particle debris (per side)!

!!! Radiation dose from hadronic shower !

!where!

! ! !r = distance from IP in meters!

! ! !) = psuedo-rapidity = - ln (tan */2)!

! ! !H = height of rapidity plateau = 0.78 s0.105!

!! !% constant for ) < 6 (* > 5 mr)!! ! !for ) > 6, H(E) —> 0 linearly @ kinematic limit!

! ! !<p+> = 0.12 log10 2E + 0.06!

! ! !s = 4 E2 !! !

Pdebris = 350 W L

10 33

!inel

90 mb E

20 TeV

D (E,r) = 26.1 Gyyr L

10 33

!inel

90 mb H(E)

7.5 p"

0.6 GeV

0.9 cosh

2.9 #r 2

Dose ! Ncollision " #inel " Charged multiplicity/event " d E

dx


Radiation damage of IR components severely limits maximum luminosity

!! Distance to first quad,

Q1: l* $ " $ ( , / G ) &

!! Let Q1 aperture = 1.5 cm ==>

At 100 TeV per beam & L = 1035 cm-2s-1

Pdebris = 180 kW/side

With no shielding

D (Q1) " 4 x 108 Gy/year ==> " 4.5 mW/g in Q1 (6 mo lifetime)

Estimate is confirmed by detailed Monte Carlo calculations

l* = 20 m E20 TeV

1/2

At L = 1035 cm-2s-1 Q1requires extensive protection with collimators


Machine protection will be challenging !! Proton colliders have enormous stored energy in their magnets & beams

* Needs many more machine sectors to keep dipole energy per sector similar to LHC * Needs many more beam abort lines to keep energy per abort line similar to LHC

!! Tunneling costs vary significantly with geography: »! Scaled costs/m for 4m diameter tunnel:

•! CERN (LEP) molasse/limestone 35 K# •! FNAL dolomite 14 K# •! Dallas chalk/marl 5 K#

30

For luminosity = 1035 cm-2s-1

Ecm (TeV) Circumference (km)

Energy in beams (GJ)

Energy in dipoles (GJ)

LHC-14 14 27 ~2 x 0.4 11

FCC-100 km* 100 100 ~2 x 11 ~180

Texas-270 km* 100 270 ~2 x 30 ~60


VLHC study conclusions for large ring: No insurmountable technical difficulties

Stage 1 Stage 2 ELN-90

Total Circumference (km) 233 233 300

Center-of-Mass Energy (TeV) 40 175 200 Number of interaction regions 2 2 2 Peak luminosity (1034 cm-2 s-1 ) 1 2 0.1

Dipole field at collision energy (T) 2 9.8 10 "* at collision (m) 0.3 0.71

Bunch Spacing (ns) 18.8 18.8 100 Interactions per bunch crossing at Lpeak 21 58 1

Psynch (W/m/beam) 0.03 4.7 1.9

Total installed power (MW) 30 250 ~150

Going to 300 km would retain proven NiTi magnet technology!


Why not about radically new acceleration techniques? Can ELN be a linear proton collider ?!

!! Imagine that Lcoll < 125 km ==> Eacc ~ 2 GeV/m ==> frf % 100 GHz!!

! ! !! ! !HD is the luminosity degradation due to space charge!! ! !D is the disruption parameter that measures the anti-pinch!

!

! ! ! ! For D < 2, the value of HD % 1.!!!

At 100 TeV/beam, "* ~ 1 m & %n ~10-6 m-rad!!

!! For f rf = 100 GHz (typical of plasmas), !z ~ 10-6 m ==> !z/"*%n %1 m-1!

!! Assume 1) bunches of 100 nC & 2) preserve emittance in the linac!

! ! ! ! rpNB ~10 - 6 m!

!! Hence at only 1033 cm-2 s-1 ==> P % 30 GW per beam!!

L (1033 cm-2 s-1) = D HD30

1 mm!z

Pbeam1 MW

D = rp NB !z

" !x,y

2 = rp NB !z

# * $n

!==> the ultimate supercollider must be a synchrotron!


Go big or go home !

!! There are no insurmountible technical obstacles to realizing a high luminosity, 100 TeV class proton collider

"! Many considerations favor building a very large ring (200 - 300 km) "! Radiation damage to detectors & IR components is a serious issue "! A 300 km synchrotrons might reach up to 0.5 PeV c.m. energy

•! Find a way to remove synchrotron radiation from the cold beam tube •! BUT is the management & sociology of such a project is practical?

!!

Nima Arkani-Hamed!

We high energy physicists have to thank Antonino Zichichi !for his deep insights, his leadership and !

his persistent dedication to a bold idea for over 50 years!

the eloisatron: physics at the energy...

Documents